Framing systems are known which include frame members arranged in a grid-like pattern for accommodating glazing panels. The frame members include a main interior portion which provides structural integrity and an exterior portion which defines glazing pockets for receiving the lateral edges of glazing panels. The frame members further typically include mounting means, such as flanges or channels, associated with mutually facing portions of the glazing pockets for mounting gaskets which engage the margins of the glazing panels to weatherseal the structure.
In certain applications it is desirable to provide a decorative cover for the exposed portion of the frame member visible from the exterior. Since the cover is provided primarily for aesthetic purposes, it is desirable to provide a cover which can be mounted to the underlying frame member without the need for exposed fasteners. One widely used type of prior art decorative cover is a snap-on cover which snaps onto the exterior portion of the frame member. The snap-on cover includes a pair of mutually opposed, rearward extending legs having inwardly projecting flanges formed thereon which engage corresponding grooves in the frame member. The cover is applied to the frame member by simply pressing the cover onto the frame member. As the legs slide onto the frame member, they are deflected outwardly, and as the flanges are brought into correspondence with the grooves on the frame member, the legs snap inwardly to engage the flanges with the grooves.
While acceptable for many applications, prior art snap-on covers suffer certain limitations which may render them unsuitable for certain applications. Since secure mounting of the snap-on cover depends upon the elasticity of the legs to bring the flanges into secure engagement with the grooves on the frame member, care must be taken that the legs are not deformed beyond their elastic limit, or yield point, as the cover is installed. Since the extent to which the legs can deflect without permanent deformation depends in large part upon the length of the legs, the cover must necessarily comprise legs which are sufficiently long to accommodate the required deflection. Consequently, snap-on covers must have a certain minimum depth which may be deeper than is aesthetically desired, and "shallow profile" covers are not possible. In addition, for those applications in which it is desired to keep the depth of the cover at or near such minimum depth, design and manufacturing tolerances, not only of the cover but also of the frame member, must be closely maintained to ensure that the legs can accommodate the degree of deflection required for snap-on installation without exceeding their elastic limit. Further, installation demands extra care, since pressing the snap-on cover onto the frame member at even a slight angle from perpendicular may bend the short legs beyond their elastic limits.